Method of drying sized molded pulp articles



Jan. 15, 1935. M, P. cHAPLlN METHOD OF DRYING SIZED MOLDED PULP ARTICLES Filed oct. 19, 1932 l//l/l/ VAcmqM Patented Jan. 15, 1931.5

UNITED STATES PATENT OFFICE METHOD F DRYING SIZED MOLDED PULP ARTICLES Merle P. Chaplin, Waterville,`Maine, assignor to Keyes Fibre Company, Inc., Waterville, Maine, a corporation of Maine Application October 19,

1 Claim.

5 water or grease proofness or both.

In my said parent application Serial No. 368,- 786, which in turn is a continuation in part of my prior application Serial No. 265,551, led March 29, 1928 issued as Patent No. 1,920,292 dated Aug. 1, 1933, I disclosed a method of an apparatus for drying 'a widely varying line of molded pulp articles such as plates, dishes, trays, packs and the like, whether'sized or unsized.

As was pointed out in said application, such a molded pulp article had been molded on standard equipment from one or more mixtures of aqueous pulp solution and when ready for drying has an appreciable moisture content depending upon such factors as the consistency of the pulp solution, the operating speed of the molding machine, the time allowed for drainage, etc.

My present application is directed to the drying and setting or fusing of the size in an article of this class where some water or grease proofing .material as rosin, wax, paraffin, casein or the like has been added to the pulp solution.

Where the pulp solution is thus sized new factors are introduced as regards drying due to the necessity of obtaining a proper setting or fusion of the wax throughout the article. Unless the sizing material is properly dispersed and set or fused throughout the article, the article will lack the desired waterproof and greaseproof characteristics.

The matter of drying the article 'while at the same time accomplishing such impregnation, dispersion or setting of the size in the article is complicated bythe fact that the articles are molded under mass production methods and consequently certain definite factors are imposed at the outset. Among these are the necessity that the ultimate article shall be saleable, meaning thereby 'that it shall have those qualities of appearance and utility which make for saleability. This -particularly applies to the finish of the article which should be a smooth finish and devoid of die marks. The articles themselves are fibrous and consequently there is a very definitel limit as to drying temperatures in the higher range necessary to accomplish the setting or fusion of the size in the article. Being made under mass production methods' an equally definite limit as to drying temperatures in the lower range is imposed since a lower drying temperature carries as its corollary a longer drying time for the ar- 1 932, serial No. 638,517

ticle on the molding machine under similar atmospheric conditions. Obviously, production schedules cannot be maintained if the article is allowed too long a drying time on the machine. Equally obviously higher heat applications with shorter drainage time i's-apt to char or burn the article. The problem therefore is to so dry the article and effect the setting or fusion of the size therein as to avoid on the one hand excessive drying temperatures, and on the other hand an excessively long drainage period. i

The article as it is draining on the forming machine is a wet soggy layer of pulp containingany where from 20 to 35% moisture. When such a wet layer is contacted by the application of a hot die thereto, the immediate eiect of the heat is to vaporize the contained moisture in the article. Such moisture must be carried away fromthe article if drying is to be rapidly effected and the sizing properly set.

According to my present concept the moisture given off at such time is accomplished by vacuum exhaustion. Such vacuum exhaustion is preferably applied at the side of the article opposite the side which is contacted by the hot die whereby to reduce the atmospheric pressure on the article progressively from the hot die side to the vacuum die side. This results in a reduction of the vapor tension causing the water or other fluid of suspension still contained in the article to be vaporized more rapidly and at lower temperatures, inducing throughout the article a thermal convection from the regions of higher boiling point towards those of lower boiling point, thus resulting in a progressive tempering of the article and setting of the size as the article is being dried as well as avoiding any tendency to bake or char the article. I thus not only obtain a better article as regards appearance of finish, but one which can be dried at materially lower temperatures, the fusion of the size being accomplished while the article is still wet and the size unset by the action of the hot water vapors being drawn through the article.

As illustrative of apparatus for the practice of my invention I show somewhat diagrammatically in the accompanying drawing a form of machine vwhich I have found highly satisfactory under actual conditions of commercial use.

In such drawing:

Fig. 1 is a vertical section through a drying unit for the practice of my invention and the production of the resultant dried smooth nished and properly sized article constituting the product of such method. and

Fig. 2 is a :z :um: indication of the progressive vapor drawing and size setting action which is induced progressively throughout the article by the simultaneous application of heat and pressure to one side of the moist article and suction to the opposite side thereof.

In Pig. 1 the numerals 1 and 2 indicate respectively a pair of relatively movable die members which when brought together in the operation of the machine define with each other a closed drying unit within which the wet article A is disposed. For the purposes of this application such article may be considered as having been die molded from an aqueous pulp solution containing a sizing material such as wax, paraiiln, casein, rosin. hydrated cellulose or the like. Similarly for the purposes of this application the die 1 may be considered as a hot pressing and smooth finishing die and the die 2 as the exhausting die, the die 1 being heated in am' suitable manner as by steam, electricity, hot air or any uid.

As here shown the'die 1 is adapted to be heated by steam, being formed with a steam chamber 3 for more effective distribution of steam over the entire article contacting and receiving face of the die. It may be suitably insulated against dissipation of the heat as indicated at 4 and is made substantially steam tight by an overlap joint on the ring 41. The exhaustion die 2 may be equipped for exhaustion through its perforated or foraminous face in any suitable manner as by vacuum or suction applied through connection 5, such die accordingly being formed as a vacuum chamber 6 beneath said foraminous article receiving face '1.

For the purposes of this application also the wet article may be considered as initially having been laid on the face of the heated die 1, one effect of the suction through exhaustion die 2 being eventually to cause transfer of the article when dried and its sizing set or fused to the article receiving face of the exhaustion die. This arrangement may be reversed, however, and the exhaustion die 2 may also be equipped with means whereby it may be heated. Obviously such die even when not equipped with special heating means of its own does become heated to some extent by reason of the thermal convection from heated die l thereto when said dies are in contact.

In any event, the wet article is confined between a pair of die umts which when brought together define a substantially tight enclosure for Y the articles during drying of the article and fusion of the sizing material. The effect of the suctionthrough die 2 is concentrated throughout the entire area of the article. Similarly, the distribution of heat from the heated article contacting face of the heated die 1 is also distributed uniformly throughout the entire area of the article. The heat and suction applications are localized, however, in the sense that they are concentrated throughout the entire extent of the article but charring or burning of the article does not result from this localization and concentration of heat at relatively high temperatures due to the fact that the suction is continuously effective to carry oiI the released vapors.

These hot water vapors are progressively drawn through the article and the sizing material is progressively set or fused from the region of maximum heat intensity in the article towards that of lower temperature range thus resulting in a tempered drying of the article and an uniform fusion of the size throughout the fibres thereof, all at lower temperatures and shorter draining times than heretofore possible without sacrice of machine speed.

The progressive drying and tempering action is indicated somewhat diagrammatically in Fig; 2, wherein the face H of the article A is the face which is contacted by the heated die 1 and the face S is the face which is contacted by the exhaustion die 2. 'Ihe heat application to the face H is an application sunicient kto produce boiling of the water of production present in the wet article and it may be as high as 400 F. and may taper off towards the suction face S of the article to a temperature as low as F.- for example. This results in a progressive or tempered drying of the article and fusion of the sizes.

Any desired degree of vacuum may be employed, a vacuum of about 25 inches mercury being suiiicient for most articles. The direct application of heat combined with the simultaneous removal of the vaporized moisture apparently causes the sizing to have a superior set of structure in the finished article as Well as imparting a smooth finish to the upper face of the article. Furthermore, the reduction of heat intensity by reducing the atmospheric pressure under which the article is dried and its sizing set appears to give a better result in the setting or tempering of the article, the combination of heat and pressure at one side of the article and vacuum exhaustion at the other side resulting in an article of superior characteristics as regards structure, finish, appearance and thoroughness of size penetration or dispersion.

By contacting the article under vacuum exhaustion with a hot die while it is moist and the sizing unset, the water proofing and grease proofing materials are more eectively distributed through and set within the article, thus resulting in a harder and smoother surface and a stronger article structure. In other words, the combined effect of the heat and contact at one side of the article and the suction at the other side of the article while the grease proofing and water proofing materials are still unset is to cause such materials to properly be dispersed through and set or fused within the brous article structure.

As illustrative of a preferred form of exhaustion die I may use the die shown in my prior Patent No. 1,709,338 as such a die maintains a circulation close to the article which will carry away the moisture as it is removed from the article and condenses. Obviously, however, other forms of vacuum kdie may be employed. Various other modications in procedure and apparatus may be Aresorted to within the spirit and scope of my invention as defined by the appended claim.

What I therefore claim and desire to secure by Letters Patent is:

The method of making a progressively tempered uniformly sized fibrous article from a liquid pulp mixture, which consists in incorporating a sizing substance into the liquid pulp mixture, in depositing by suction a layer of pulp from such liquid pulp mixture onto a perforated forming die, and in subsequently contacting said pulp layer at one side withI a hot die while said pulp layer is still moist and the sizing substance still unset to dry the pulp layer and fuse the sizing substance while simultaneously applying vacuum to the other side of said pulp layer to induce a thermal convection from the regions of higher boiling point towards those of lower boiling point.

MERLE CHAPLIN. 

